1. Field of the Invention
This invention relates to polyorganosiloxane gels. More particularly, this invention relates to container surfaces and other substrates that are in contact with polyorganosiloxane gels and to a method for treating these substrates to prevent the migration of bubbles from these substrates into the gel.
2. Background Information
Polyorganosiloxane gels are useful in numerous applications, including mammary prosthesis, as damping media and for the encapsulation of delicate electronic devices and circuits to protect them against damage by moisture and mechanical shocks. The use of polyorganosiloxanes as the light transmitting medium for a compressible optical waveguide device is disclosed in U.S. Pat. No. 4,128,299, which issued to J. Maher on Dec. 5, 1978, and in copending U.S. patent application Ser. No. 592,481 filed on Mar. 23, 1984.
Cured polyorganosiloxane gels are characterized as being relatively soft and deformable in comparison to polyorganosiloxane elastomers and resins. The cured gels are typically too soft to exhibit hardness values on any of the Shore durometer scales. Polyorganosiloxane gels are often characterized in terms of penetration values that are typically expressed as the depth to which the surface of the gel is depressed by a specified loading. Typical penetration values are within the range of from 1 to 10 mm or higher under a loading of 20 g. applied using a 1.6 cm.-diameter spherical foot.
If the gel is to be used as a light transmitting medium, it is often required that the cured gel remain optically clear and free of bubbles or other defects that could alter the optical properties of the gel. When a gel is in contact with a substrate such as the inner surface of a molded or extruded container exhibiting contour variations and/or irregularities, these variations and irregularities can serve as nucleation sites at which gases dissolved in the gel or trapped between the gel and the substrate can form bubbles. The gas can be air that becomes entrapped when the substrate is covered with the gel.
Irrespective of the means by which gaseous materials arrive at the surface of a substrate, bubble formation can occur when these gaseous materials contact potential nucleation sites present on the substrate. The elasticity of the gel allows bubbles to expand and/or coalesce as they migrate into the gel. The end result of this migration can be an irreversible alteration of the optical properties of the cured gel. The gel or the entire device or article must then be replaced, a costly and time consuming procedure.
Copending U.S. patent application Ser. No. 625,939, filed on June 29, 1984 teaches that bubble formation at the interface between a gel and a solid nonflowable substrate can be prevented by coating the substrate with a layer of an uncured extrudable silicone rubber composition that is compatible with the gel and becomes cohesively bonded thereto during simultaneous curing of the rubber and the gel by a platinum catalyzed hydrosilation reaction. It has now been found that while this technique substantially reduces the migration of bubbles into the gel composition, it does not eliminate it under conditions that may be encountered during the fabrication and use of gel containing devices.